Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2011

Dec. 31, 2010

Fair Value Measurement Abstract

Fair Value of Assets Measured on a Recurring Basis

Assets and liabilities measured at fair value on a recurring basis at December 31, 2011 are as follows:

	Fair value measurements						Total fair value
In millions	Level 1		Level 2		Level 3
Assets:
Cash and cash equivalents	$	1,160.7	$	—	$	—	$	1,160.7
Marketable securities	10.4		—		—		10.4
Derivative instruments	—		9.3		—		9.3
Benefit trust assets	13.3		156.2		—		169.5
Total	$	1,184.4	$	165.5	$	—	$	1,349.9
Liabilities:
Derivative instruments	$	—	$	22.2	$	—	$	22.2
Benefit trust liabilities	15.9		162.4		—		178.3
Total	$	15.9	$	184.6	$	—	$	200.5

Assets and liabilities measured at fair value on a recurring basis at December 31, 2010 are as follows:

	Fair value measurements						Total fair value
In millions	Level 1		Level 2		Level 3
Assets:
Cash and cash equivalents	$	1,014.3	$	—	$	—	$	1,014.3
Marketable securities	15.5		—		—		15.5
Derivative instruments	—		21.5		—		21.5
Benefit trust assets	17.3		155.2		—		172.5
Total	$	1,047.1	$	176.7	$	—	$	1,223.8
Liabilities:
Derivative instruments	$	—	$	2.6	$	—	$	2.6
Benefit trust liabilities	17.4		178.4		—		195.8
Total	$	17.4	$	181.0	$	—	$	198.4